Multiplication of M. leprae has been obtained in vitro, and continued for nine passages at 30-60 day intervals. Best numbers per milliliter have been disappointing, leveling off at 1x10-6 - 1x10-7 per milliliter. It may be necessary to develop a continuous growth, large volume fermentor system to acquire milligram or gram amounts of wet or dry growth. Growth adjuvants are being used in an attempt to increase the growth rate as well as the cell harvest. We were unable to duplicate the culture results of Murohashi and Yoshida; our results using their procedures were completely negative. A new species of mycobacterium, an "armadillo-derived mycobacterium" (ADM), has also grown out. We can quickly differentiate it from M. leprae by pyridine decolorization, which renders M. leprae, but not the ADM, non-acid-fast. The ADM has been found susceptible to kanamycin, amikacin, streptomycin, rifampin, and tetracycline. We are using kanamycin at 10 mcg/ml to eliminate it from our M. leprae cultures.